Blue Ridge Paper Products BART determination
1.0 Introduction .................................................................................................................... 3
1.1 BART Determination .........................................................................................3
2.0 General Description......................................................................................................... 5
2.1 BART Affected Units .........................................................................................5
2.2 BART Exemption Modeling Analysis ............................................................... 6
3.0 Regulatory Analysis ........................................................................................................ 8
3.1 Federal BART Applicability and Required Analyses…………………………..8
3.2 North Carolina BART Applicability…………………….……………………...9
3.3 Required Air Quality Permits…………………………………………………...9
4.0 Best Available Retrofit Technology Analysis................................................................. 10
4.1 Summary .............................................................................................................10
4.2 BART Analysis Overview............................................. .....................................10
4.3 BART Analysis for Recovery Boilers................................................................. 13
4.3.1 BART Analysis for NOx emission control.............................................. 13
4.3.2 BART Analysis for SO2 emission control.............................................. 15
4.4 BART Analysis for Smelt Dissolving Tanks ...................................................... 17
4.4.1 BART Analysis for SO2 and PM emissions control............................... 17
4.4.2 Bart Analysis for NOx emission control ................................................. 18
4.5 BART Analysis for Black Liquor Oxidation System.......................................... 18
Response to EPA and NPS Comments on BART Permit Application ....... ........... APPENDIX A
NCASI Corporate Correspondents Memorandum on Retrofit controls ....... ........... APPENDIX B
Public Notice for BART Title V Air Permit Modification .......................... ........... APPENDIX C
Blue Ridge Paper Products BART determination
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The Blue Ridge Paper Products= (BRPP) Canton facility is a bleached kraft pulp mill producing
bleached kraft softwood and hardwood pulp, paper and paperboard. Existing sources include:
five power boilers, a batch digester and brownstock washer system, two recovery boilers, black
liquor evaporator system, turpentine recovery system, two lime kilns, a chlorine dioxide
generator, two pulp bleaching systems, three paper machines and a paperboard dryer. The
facility is a Title V facility and operates under air permit 08961T08. BRPP submitted a BART
evaluation Permit Application to the North Carolina Department of Environment and
Environmental Resources Division of Air Quality Division of Air Quality (NCDAQ) on
November 16, 2007.
The requirements for Best Available Retrofit Technology (BART) are set forth in 15A NCAC
2D .0543 “Best Available Retrofit Technology.” This rule, currently State-Only enforceable,
implements the BART provisions of 40 CFR 51.301 for emission sources that may cause or
contribute to any visibility impairment in a mandatory Class I federal areas as determined using
40 CFR 51, Subpart P. “BART-eligible” sources are those sources built between 1962 and 1977
that have the potential to emit more than 250 tons per year of one or more visibility-impairing
compounds including sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matter (PM), and
volatile organic compounds (VOCs), and that fall within 26 industrial source categories
(including Kraft pulp and paper manufacturing). A review of the emission sources found that
there were five emission sources that were BART eligible: Recovery Boiler 10, Recovery Boiler
11, No. 10 smelt dissolving tank, No. 11 smelt dissolving tank, and the Black Liquor Oxidation
System.
Under the authority of 15A NCAC 2D .0543(c), a BART-eligible source can be exempted from
the BART requirements based on dispersion modeling demonstrating that the source cannot
reasonably be anticipated to cause or contribute to visibility impairment in a Class I area. The
emissions from these sources were modeled using CALPUFF to determine if the emissions from
the BART eligible emission sources contributed to perceptible visibility impairment to Class I
areas. The results of this modeling indicated that there was a significant impact from these
sources to the Great Smokey Mountains and the Shining Rock Class I areas. Since these
emission sources could not be otherwise exempted from BART, a BART analysis was
conducted in accordance with the requirements set forth in 15A NCAC 2D .0543.
The NCDAQ has made the determination that BART for the affected emission sources is no
additional controls. Therefore, the NCDAQ proposes to issue an air permit with a specific permit
condition that notes that the permittee has satisfied all of the requirements for BART and that no
additional controls are necessary. The remainder of this report contains a review by NCDAQ of
the demonstration and analyses presented by Blue Ridge Paper Products. The response to EPA
and the National Park Service comments on the BART Permit application may be found in
Appendix A. Appendix B contains the NCASI Corporate Correspondents Memorandum on
Blue Ridge Paper Products BART determination
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retrofit controls.
BART will be implemented through a modification to Blue Ridge Paper Products Title V air
permit. The Title V air permit application implementing BART must undergo adequate public
participation. The NCDAQ solicits and encourages participation by the general public, industry,
and other affected persons. Specific public notice requirements and a 30-day public comment
period are required before the NCDAQ can take final action on this application. Appendix C
contains a copy of the public notice.
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“BART-eligible” sources are those sources built between 1962 and 1977 that have the potential
to emit more than 250 tons per year of one or more visibility-impairing compounds including
sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matter (PM), and volatile organic
compounds (VOCs), and that fall within 26 industrial source categories (including Kraft pulp and
paper manufacturing). The Blue Ridge Paper Canton Mill has 5 BART-eligible units:
• The No. 10 Recovery furnace has a nominal black
liquor solids firing rate of 121,000 pounds of black liquor solids per hour and can fire fuel oil
during start-up, shutdown, and malfunction (SSM) at a nominal heat input rate of
382 MMBtu/hr. The unit is controlled by an electrostatic precipitator. This unit is subject to
MACT standards at 40 CFR 63, Subpart MM, and its PM emissions are approximately 10
percent of the single source recovery furnace limit of 0.044 gr/dscf. The unit was
constructed in 1964.
• The No. 11 Recovery furnace was constructed in 1973
and has a nominal black liquor solids firing rate of 121,000 pounds of black liquor solids per
hour and can fire fuel oil during start-up, shutdown, and malfunction (SSM) at a nominal
heat input rate of 382 MMBtu/hr. The unit is controlled by an electrostatic precipitator. This
unit is subject to MACT standards at 40 CFR 63, Subpart MM, and its PM emissions are
approximately 15 percent of the single source recovery furnace limit of 0.044 gr/dscf.
• This smelt dissolving tank serves the No. 10
Recovery Furnace and was installed in 1964. This unit is controlled by a chevron mist
eliminator. This unit is subject to MACT standards at 40 CFR 63, Subpart MM.
• This smelt dissolving tank serves the No. 11
Recovery Furnace. This unit is controlled by a chevron mist eliminator. This unit is subject
to MACT standards at 40 CFR 63, Subpart MM. The unit was constructed in 1973.
• The black liquor oxidation system precedes the
two recovery furnaces and is in place to reduce Total Reduced Sulfur (TRS) emissions from
the recovery furnaces by oxidizing the black liquor. This system is controlled by a
Regenerative Thermal Oxidizer (RTO) and wet scrubber; therefore, the RTO scrubber stack
parameters and emission rates were included in this analysis. This unit is subject to MACT
standards at 40 CFR 63, Subpart S, via 40 CFR 63.94, Equivalency by Permit. The BLOX
system was originally installed in 1964.
These units are part of the mill’s chemical recovery system, which is an integral part of the Kraft
pulping process. Although the recovery furnaces do produce steam for process operations, their
primary purpose is chemical recovery, and are collectively controlled below the chemical
recovery source MACT emission limits set forth in 40 CFR 63 Subpart MM. In addition, the
BLOX will be controlled by a regenerative thermal oxidizer (RTO) to reduce HAP emissions
under MACT Subpart S, followed by a wet scrubber to minimize SO2 emissions from
combustion of sulfur compounds in the BLOX gases in order to not be considered a signicicant
Blue Ridge Paper Products BART determination
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modification under NSR PSD. Therefore, the 5 BART-eligible emission units at the Blue Ridge
Canton Mill are already well-controlled units.
The first step of the BART process was to determine if any of the affected BART-eligible
sources could be exempted based on their contribution to visibility impacts on Class I areas.
According to 40 CFR Part 51, Appendix Y, a BART-eligible source is considered to “contribute”
to visibility impairment in a Class I area if the modeled 98th percentile change in deciviews1 (dv)
is equal to or greater than the “contribution threshold.” The contribution threshold is understood
to be 0.5 deciview and a threshold of 1.0 deciview is understood to cause visibility impairment.
Any BART-eligible source determined to cause or contribute to visibility impairment in any
Class I area is subject to a BART evaluation.
Blue Ridge submitted a modeling protocol to NCDAQ on January 31, 2006. The objective of the
modeling protocol was to obtain approval from NCDAQ on the modeling procedures that were
used to conduct the BART exemption modeling for the Blue Ridge Canton Mill. The protocol
incorporated guidance developed by VISTAS for conducting a BART modeling analysis and
proposed a more refined line-of-sight modeling approach. The protocol presented detailed
explanations of both modeling procedures. However, the BART determination was based on the
VISTAS modeling protocol. The results of the exemption modeling of the combined BART
eligible units are shown in the following table.
Shining Rock 2.887
Great Smoky Mountains 0.764
Linville Gorge 0.155
Joyce Kilmer 0.134
Cohutta 0.095
1 – Delta deciview as compared to natural conditions.
1 means a measurement of visibility impairment. A deciview is a haze index derived from calculated light
extinction, such that uniform changes in haziness correspond to uniform incremental changes in perception across
the entire range of conditions, from pristine to highly impaired. The deciview haze index is calculated based on the
following equation (for the purposes of calculating deciview, the atmospheric light extinction coefficient must be
calculated from aerosol measurements):
Deciview haze index=10 lne(bext/10 Mm−1).
Where bext=the atmospheric light extinction coefficient, expressed in inverse megameters
(Mm−1).
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The results of the exemption modeling indicate that, since the emissions from the BART eligible
emission sources exceed the 0.5 dv contribution threshold for two Class I areas, a BART
evaluation must be conducted for each of the five emission sources.
Blue Ridge Paper Products BART determination
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The Clean Air Act established goals for visibility in many national parks and wilderness areas.
Through the 1977 amendments to the Clean Air Act, Congress set a national goal for visibility as
“the prevention of any future, and the remedying of any existing, impairment of visibility in
mandatory Class I Federal areas which impairment results from manmade air pollution.” The
Amendments required EPA to issue regulations to assure “reasonable progress” toward meeting
the national goal. The Class I Areas affected by this facility are the Shining Rock and the Great
Smoky Mountains National Parks.
One of the principal elements of the visibility protection provisions of the Clean Air Act
addresses installation of best available retrofit technology (BART) for certain existing sources.
“BART-eligible” sources are those sources built between 1962 and 1977 that have the potential
to emit more than 250 tons per year of one or more visibility-impairing compounds including
sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matter (PM), and volatile organic
compounds (VOCs), and that fall within 26 industrial source categories (including Kraft pulp and
paper manufacturing).
The BART requirements are found in 40 CFR 51.308(e) “
In addition, the final BART
implementation and guidance (40 CFR Part 51, Appendix Y) published on July 6, 2005 and
allow for a BART evaluation for any BART-eligible source that “emits any air pollutant which
may reasonably be anticipated to cause or contribute to any impairment of visibility” in any
mandatory Class I federal area. The guidance (Appendix Y) must only be followed by states for
large fossil fuel fired electric steam generators, but is otherwise optional for other potential
BART units.
According to Appendix Y, a BART-eligible source is considered to “contribute” to visibility
impairment in a Class I area if the modeled 98th percentile change in dv is equal to or greater
than the “contribution threshold.” The contribution threshold is understood to be 0.5 deciview
and a threshold of 1.0 deciview is understood to cause visibility impairment. Any BART-eligible
source determined to cause or contribute to visibility impairment in any Class I area is subject to a
BART evaluation.
Based on the results of the BART evaluations, States will develop Regional Haze State
Implementation Plans (SIPs). States must submit plans to implement the Regional Haze Rule for
EPA review and approval by January 2008.
Blue Ridge Paper Products BART determination
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The BART requirements are implemented through 15A NCAC 2D .0543 “Best Available
Retrofit Technology.” This rule implements the BART provisions of 40 CFR 51.301 for
emission sources that may cause or contribute to any visibility impairment in a mandatory Class
I federal area as determined using 40 CFR 51, Subpart P. There five emission sources that are
BART eligible: Recovery Boiler 10, Recovery Boiler 11, No. 10 smelt dissolving tank, No. 11
smelt dissolving tank, and the Black Liquor Oxidation System.
Under the authority of 15A NCAC 2D .0543(c), a BART-eligible source may be exempted from
the BART requirements based on dispersion modeling demonstrating that the source cannot
reasonably be anticipated to cause or contribute to visibility impairment in a Class I area. The
results of this modeling indicated that there was a significant impact from these sources to the
Great Smokey Mountains and the Shining Rock Class I areas. Since these emission sources
could not be otherwise exempted from BART, a BART analysis was conducted in
accordance with the requirements set forth in 15A NCAC 2D .0543.
The BART requirements, if any, will be implemented through the Title V permitting process.
Since BART will not be required for any of the BART-eligible sources, the Title V permit will
be modified to indicate that there are no applicable BART requirements for the BART-eligible
emission sources at Blue Ridge Paper products.
Blue Ridge Paper Products BART determination
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The sources subject to the Best Available Retrofit Technology (BART) requirements include the
two recovery boilers, their associated smelt dissolving tanks, and the BLOX. This section
presents the BART analyses for these emission sources, since they could not be otherwise
exempted based on emission modeling. This BART evaluation has concluded that BART for all
of these emission sources are the existing emission control systems.
BART is defined as follows [40 CFR 51.301]:
means an emission limitation based on the degree
of reduction achievable through the application of the best system of continuous emission
reduction for each pollutant which is emitted by an existing stationary facility. The emission
limitation must be established, on a case-by-case basis, taking into consideration the technology
available, the costs of compliance, the energy and non-air quality environmental impacts of
compliance, any pollution control equipment in use or in existence at the source, the remaining
useful life of the source, and the degree of improvement in visibility which may reasonably be
anticipated to result from the use of such technology.”
The BART analysis was conducted with consideration of the six requirements identified above
and the five steps identified in 40 CFR 51 Appendix Y “Guidelines for BART Determinations
Under the Regional Haze Rule.” Again, these guidelines are not the exclusive means of defining
BART for facilities other than Electric Generating Units. However, they provide a convenient
structure to consider.
• Step 1—Identify All Available Retrofit Control Technologies,
• Step 2— Eliminate Technically Infeasible Options,
• Step 3— Evaluate Control Effectiveness of Remaining Control Technologies,
• Step 4— Evaluate Impacts and Document the Results, and
• Step 5—Evaluate Visibility Impacts.
Each of these steps is discussed in further detail in the sections presented below.
Step 1 – Identify All Available Retrofit Control Technologies
Appendix Y to 40 CFR 51 defines an available retrofit control option as an air pollution control
technology with a practical potential for application to the emissions unit and the regulated
pollutant under evaluation. Technologies available for compliance with Best Available Control
Blue Ridge Paper Products BART determination
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Technology (BACT) or Lowest Achievable Emission Rate (LAER) regulations should be
included as part of the BART analysis. Furthermore, technologies that are evaluated should
include existing controls for the source category in question as well as the transfer of controls
that have been applied to similar source categories and gas streams. However, control
technologies which have not yet been applied to full scale operations are not required to be
included in the evaluation.
Potentially applicable control technologies can be grouped into one of three categories:
• Pollution Prevention. As stated in the regulation this is “
”
• Add-on Control Technologies. “
”
• Combinations of the previous two categories.
Sources that were used to determine the potentially applicable control technologies for the Blue
Ridge BART analysis include the Environmental Protection Agency’s RACT/BACT/LAER
Clearinghouse (RBLC), control technology vendors, and information supplied by the National
Council for Air and Stream Improvement (NCASI).
Step 2 – Eliminate Technically Infeasible Options
Step 1 of the BART analysis identifies all of the control technologies that are potentially
available for the BART eligible emission units. In step 2 of the analysis this list is further
refined to include only those technologies that are technically feasible. Appendix Y of 40 CFR
51 defines a technically feasible control technology as:
Control technologies that are deemed technically infeasible in this step of the evaluation must
include specific data stating that the technology is either commercially unavailable or outline the
specific circumstances which preclude is application. Facilities may demonstrate that a
particular technology is infeasible due to “
”
Implications of cost effectiveness should not be included in this step of the analysis.
Blue Ridge Paper Products BART determination
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Step 3 – Evaluate Control Effectiveness of Remaining Control Technologies
Control technologies determined to be technically feasible in step 2 of the analysis are further
evaluated in step 3. The two main issues in step 3 of the process are as follows:
• Making sure that you express the degree of control using a metric that ensures an “apples to
apples” comparison of emissions performance levels among options, and
• Giving appropriate treatment and consideration of control techniques that can operate over a
wide range of emission performance levels.
The analysis should be based on the maximum level of control that a technology is capable of
achieving.
Step 4 – Evaluate Impacts and Document the Results
For the control technologies determined to be commercially available and technically feasible,
the affected facility must conduct the following analyses to select the control technology that
meets the requirements of BART.
The analysis evaluates four impacts that would potentially result from the installation of a control
technology.
Impact analysis part 1: Costs of compliance,
Impact analysis part 2: Energy impacts,
Impact analysis part 3: Non-air quality environmental impacts, and
Impact analysis part 4: Remaining useful life.
Appendix Y to 40 CFR 51 presents detailed guidance for conducting the evaluation of each
potential impact. The analysis presented later in this section for each available and technically
feasible control technology identified for the BART eligible emission units follows these
guidelines.
Step 5 – Evaluate Visibility Impacts
Once the facility has completed the steps outlined above and an available, technically feasible
control technology has been selected, then the visibility improvements are evaluated in this final
step.
Baseline emissions and the visibility impacts are compared to the predicted visibility impacts
from the emission sources with the control technology installed. If the net visibility
improvement is less than that which would contribute to visibility impairment (as defined in the
preamble to Appendix Y) then there is no need for the facility to implement the control
technologies because the resulting visibility impacts would be negligible.
Blue Ridge Paper Products BART determination
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Blue Ridge operates two recovery furnaces at the Blue Ridge Canton Mill. Each unit is
permitted to fire 121,000 pounds of black liquor solids per hour. The units are capable of firing
fuel oil during startup, shutdown, and malfunction. Each unit is currently equipped with an
electrostatic precipitator (ESP), and the emissions from each of these units exceed the PM
control requirements of 40 CFR 63, Subpart MM (MACT II).
It is important that the use and function of the recovery furnace in the pulp and paper process is
properly understood. The recovery furnace performs the following functions:
• Evaporates residual moisture from the black liquor solids,
• Combusts organic constituents in the black liquor,
• Reduces oxidized sulfur compounds to sulfide,
• Recovers inorganic chemicals (smelt) in molten form. This smelt is dissolved in the smelt
dissolving tanks and returned to the process,
• Conditions the products of combustion to minimize chemical carryover, and
• Generates additional steam for mill processes.
The primary purpose of a recovery furnace is not to produce steam, but for chemical recovery
that is inherent to the operation of the Kraft pulping process with steam a byproduct.
The recovery furnaces emit PM, SO2, and NOx. Each of these units are equipped with an ESP
that exceeds the particulate emission requirements of 0.044 gr/dscf at 8% O2 for MACT 40 CFR
63 Subpart MM. Recent stack testing performed to demonstrate compliance with MACT
Subpart MM showed particulate emissions of 0.004 gr/dscf at 8% O2 for No. 10 Recovery
Furnace and 0.007 gr/dscf at 8% O2 for No. 11 Recovery Furnace. Therefore, potential retrofit
control technologies for particulate matter emissions from the recovery furnaces were not further
evaluated since the units are already equipped with the most stringent controls and the operation
of these controls is required by the facility’s Title V Operating Permit.
Compared to a typical power boiler, emissions of NOx from a recovery furnace are generally
quite minimal. The minimal NOx emissions can be attributed to four main mechanisms within
the furnace.
• The as-fired nitrogen content of most black liquor solids is less than 0.2% by weight.
• The temperature profiles within the furnace generally do not promote the formation of
thermal NOx.
• The introduction of combustion air within the furnace is staged.
There are several NOx control technologies that are potentially applicable to combustion sources
based on reviews of similar processes and a review of the RBLC database.
1. Low NOx Burners (LNB) – The use of low NOx burners is a demonstrated technology
installed on many fossil-fuel combustion sources. However, this is not a demonstrated
Blue Ridge Paper Products BART determination
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technology for a recovery furnace. Black liquor has a large amount of water.
Consequently, the drying, pyrolysis, and char burning of liquid droplets occurs over an
extended trajectory from the liquor guns to the char bed. Therefore, the benefits of a low
NOx burner would not be realized in a recovery furnace. Furthermore, the recovery
furnace is already equipped with primary, secondary, and tertiary air which provides
inherent NOx control.
2. Flue Gas Recirculation (FGR) – FGR involves the recirculation of a portion of the
exhaust gas back into the combustion zone of the furnace. This control technology is
aimed toward minimizing the formation of thermal NOx. However, as previously stated
thermal NOx emissions from a recovery furnace are minimal. Therefore, installation of
this control technology would not result in significant NOx reductions and is not
considered further.
3. Water Injection – This control technology is generally applied to natural gas-fired boilers
for the control of NOx emissions. The introduction of water droplets into the combustion
zone of a recovery furnace could lead to an explosive condition inside the unit.
Therefore, water injection is not technically feasible.
4. Add-on NOx Controls – This category involves the evaluation of both Selective Non-
Catalytic Reduction (SNCR) and Selective Catalytic Reduction (SCR). In the SNCR
process, urea or ammonia would be injected into the recovery furnace. No long-term
evaluations have been conducted for a SNCR installation on a recovery furnace. Since
the primary purpose of the recovery furnace is chemical recovery there are concerns that
the introduction of additional chemicals into the process could have a harmful effect on
the quality of the smelt produced.
SCR involves passing the exhaust stream over a catalyst to reduce NOx emissions. The
SCR system can either be installed prior to the ESP (High Dust application) or after the
ESP (either hot side or cold side). The problem associated with this control technology
involves possible catalyst fouling from entrained particulate if the unit were installed
prior to the ESP. If the SCR were installed after the ESP, the gas stream will be too cool
to effectively react with the NOx without flue gas reheating. Therefore, both of these
options are considered technically infeasible.
5. Staged Combustion – This involves adding a quaternary zone of combustion air within
the recovery furnace. There have been limited demonstrations of this technology on a
short-term basis. A 20-40% reduction in NOx emissions was observed. Therefore, this
control technology is the only option identified as technically feasible for NOx reduction
from recovery furnaces and has been evaluated further as part of the BART process.
Mill personnel investigated the potential installation of within each recovery
furnace along with the installation of new liquor fuel guns. Cost estimates provided by Mill
personnel indicate that the total capital costs associated with the modification would be
approximately $9 million for both furnaces. In addition to the capital and installation costs, each
recovery furnace would be out of service for one month while the modification was being made.
Therefore, during these periods, the pulp mill could only operate at one-half capacity and the
mill would have to purchase dry furnish at a cost of approximately $23.1 million in order to
maintain paper production. Therefore, the total costs associated with the implementation of this
Blue Ridge Paper Products BART determination
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control technology on both furnaces are $32.1 million. The annualized costs for NOx removal
were estimated to be $3,839,996 for each recovery boiler.
Based on an expected NOx reduction efficiency of 40% (a reduction of 230 tons per recovery
furnace), the cost effectiveness per ton of NOx removed using would be
approximately $16,700 per ton.
There are no additional impacts anticipated from the modification (i.e., water, additional power,
etc.).
The anticipated visibility impacts from a 40% reduction in NOx emissions from the recovery
furnaces were estimated to be a 0.371 deciview improvement over the current conditions. The
cost of this retrofit would be extremely high, at $44,994/ton/dv.
The number of days with an estimated visibility greater than 0.5 deciview impact at the baseline
operating conditions was estimated to be 86 days at Shining Rock and 18 days at Great Smoky
Mountains. The installation of quaternary air in the recovery furnaces would only slightly
reduce the number of days greater than 0.5 deciview impact at Shining Rock to 82 days and 15
days at Great Smoky Mountains.
Based on the above analysis, theNCDAQbelieves that the installation of NOx reduction controls
for the recovery furnaces is not economically feasible.
The inlet loading of sulfur is significant, normally in the range of 3-5% by weight. One of the
primary purposes of the recovery furnace is to recover and convert oxidized sulfur compounds to
sulfide. The majority of this sulfur is contained in the smelt leaving the furnace; however, a
small fraction of the compound can be emitted in the form of SO2. There are a number of factors
which are thought to influence the formation of SO2 in the recovery furnace; however, a direct
relationship has not been established.
A review of the RBLC database shows that there are no add-on control technologies that have
been installed solely for the control of SO2 emissions.
An additional source of information on emissions controls is the National Council of Air and
Stream Improvement (NCASI) Corporate Correspondents Memorandum CC 06-014 entitled
“
” A copy of this memorandum is included in As the
environmental control reference organization for the pulp and paper manufacturers, NCASI
follows the industry closely and is aware of the control measures that are currently employed.
This document further iterates that there are no control measures specific to SO2 employed by
the pulp and paper industry on recovery furnaces. According to NCASI, the few wet scrubbers
that have been installed on recovery furnaces in the pulp and paper industry have been installed
for additional particulate control following an ESP (e.g., for PSD avoidance), although there is
some residual SO2 removal from the units.
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However, the installation of a wet scrubber following the ESP on a recovery furnace is
technically feasible, although it would be a complicated and costly retrofit for the recovery
furnaces at the Blue Ridge Canton Mill. Once a technically feasible control technology has been
determined, it is necessary to begin evaluating the additional impacts as described in step 4 of the
BART procedures.
The first impact to be evaluated is the potential cost associated with the installation of the
scrubber. Vendors were contacted by the mill for a similar project and given information
regarding the composition of the gas stream and the estimated volumetric flow rate. The cost of
a wet scrubber was obtained from Monsanto Enviro-Chem. Based on this budgetary capital cost
estimate, additional expenses associated with installation of the device were estimated. The
source of these estimates is both historical mill experience and EPA’s Control Cost Manual. It is
important to note that the Blue Ridge Canton Mill was originally constructed in 1905, and
subsequent modifications have left the facility extremely “land-limited.” The ESPs for the two
furnaces are located on the top of the recovery building, but there is no room on the roof of this
building for two scrubbers. Therefore, the installation of a new scrubber on each recovery
furnace would require extensive piping and ductwork modifications. The closest location to the
recovery furnaces for the possible installation of a scrubber would require over 300 feet of
stainless steel ductwork including a bridge to elevate the ductwork over roadways. Additionally,
a new fan would be required to move the exhaust through the new ductwork and scrubber to
overcome the additional pressure loss. Not only would there be capital costs associated with the
installation of a fan, but the current power distribution system is operating at maximum capacity
and a new switch gear would be required.
The expenses associated with the wet scrubber includes capital costs associated with the
purchase and installation of the new equipment and the cost associated with the purchase of pulp
to replace lost production during the period of construction. The capital costs for the installation
of a wet scrubber achieving 90% SO2 removal from a recovery boiler was estimated to be
$26,293,000, and annualized costs at $6,897,430. The cost effectiveness per ton of SO2 removed
was estimated at $13,643 per ton. Incremental cost effectiveness per ton of pollutant removed
was not calculated because only one control technology has been identified as technically
feasible.
Operation of a wet scrubber will have an impact on energy consumption and will have secondary
environmental impacts to the air, water, and soil. Operation of the scrubber will require
additional electricity. This power would either be generated onsite or be purchased from the grid
and would have an associated air emissions impact from either the onsite boilers or the power
generation facility located nearby. In addition, the wet scrubber system will require additional
water usage and will generate gypsum (calcium sulfate) that will require solid waste disposal.
As outlined in the BART evaluation process, the final step that must be conducted is the
evaluation of potential improvements to visibility.
The results of the visibility analysis resulting from the installation of wet scrubbers on the
recovery boilers and the current configuration for the smelt dissolving tanks and the BLOX
system demonstrates that the installation of wet scrubbers on the recovery furnaces does not
result in a visibility improvement at the Shining Rock Class I area. This scenario actually causes
Blue Ridge Paper Products BART determination
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a higher delta deciview impact than the modeled current conditions. The number of days with an
estimated visibility greater than 0.5 deciview at the baseline operating conditions was 86 days at
Shining Rock and 18 days at Great Smoky Mountains. The installation of wet scrubbers would
actually increase the number of days greater than 0.5 deciview impact at Shining Rock to 91
days. However, a slight decrease may be seen at Great Smoky Mountains with only 9 days
greater than 0.5 deciview impact.
The smelt generated in the recovery furnaces is discharged into a tank where large chunks are
broken into smaller pieces by a steam jet. Weak wash water is added to the vessel to create
green liquor which is further processed in the causticizing system to create white liquor for reuse
in the pulping process. There are minimal emissions of NOx, SO2, and particulate from the smelt
dissolving tanks. Blue Ridge Paper does not have site-specific NOx and SO2 measurements from
the smelt tanks, but is using published emission factors from NCASI Technical Bulletin 884 to
estimate emissions of these compounds. As no combustion occurs in the smelt tanks, NCASI
believes that the small emissions of NOx and SO2 sometimes measured may be a result of
oxidation of ammonia emissions within the NOx analyzer and oxidation of sulfur in the smelt
during smelt-water explosions. Each unit is currently equipped with a chevron mist eliminator
for reduction of emissions of particulate and complies with MACT standards for PM.
A review of the RBLC database indicates that smelt dissolving tanks located at other pulp and
paper facilities utilize proper operation and wet scrubbers for the minimization of particulate and
SO2 emissions. However, emissions from these units are minimal and are emitted at relatively
low velocities which limits the control technologies that are technically feasible. Blue Ridge
personnel have investigated improvements to the current control system design that involve
installation of “micro mist” nozzles to improve the PM control efficiency. Capital costs
associated with the scrubber upgrades for a 50% removal in both PM and SO2 are estimated at
$250,000 per scrubber, with an annualized cost of $197,862. The estimated cost effectiveness
for 50% SO2 control is $301,160/ton SO2 removed. The estimated cost effectiveness for 50%
PM control is $13,862.
As was done for the previously evaluated technically feasible control technologies, the visibility
improvements that may be obtained from modifications to the current smelt tank scrubbers was
investigated. A 50 percent improvement over current SO2 and PM emissions would result in a
0.029 deciview improvement could be seen after modifying the scrubbers. The cost is
$10,384,813/ton/dv for SO2 and $478,016/ton/dv for particulate.
Blue Ridge Paper Products BART determination
18
The number of days with an estimated visibility greater than 0.5 deciview impact at the baseline
operating conditions is 86 days at Shining Rock and 18 days at Great Smoky Mountains. The
installation of micromist scrubbers on the smelt tanks would only minimally reduce the number
of days greater than 0.5 deciview impact at Shining Rock to 79 days and 17 days at Great Smoky
Mountains.
Based on the above analysis, the NC DAQ believes that the installation of retrofit controls on the
smelt dissolving is not economically feasible.
.
There are no control technologies to reduce NOx emissions that are available for installation on a
smelt dissolving tank. A review of the RBLC database shows that only proper operation and
good recovery furnace combustion techniques have been determined as BACT for NOx
emissions from smelt tanks. NCASI is not aware of any smelt tanks with NOx controls installed.
Therefore, no further evaluation was conducted for NOx control technologies for the smelt
dissolving tanks.
On April 15, 1998, the EPA promulgated National Emission Standards for Hazardous Air
Pollutants (NESHAP) from the Pulp and Paper Industry (40 CFR 63, Subpart S). Under
40 CFR 63.94, the North Carolina Department of Environment and Natural Resources (NC
DENR) requested approval from EPA to implement alternative requirements in the form of
permit terms and conditions instead of the requirements in 40 CFR 63, Subpart S. This alternate
process is called equivalency by permit (EBP). The EPA has approved this request with an
effective date of June 11, 2004. Blue Ridge Paper submitted an application on June 17, 2004 to
request approval of an alternate compliance approach to that required in 40 CFR Subpart S for
the high-volume, low-concentration (HVLC) sources (referred to as MACT I, Phase 2).
This alternate compliance approach, which was approved by EPA on March 10, 2005, will allow
the Blue Ridge Canton Mill to achieve a greater level of hazardous air pollutant (HAP) emission
reduction, additional significant environmental benefits such as total reduced sulfur (TRS)
compound emissions reductions, and community/industrial economic sustainability results not
achieved under 40 CFR 63.443. In lieu of controlling pulp mill HVLC sources under 40 CFR
63.443, the Blue Ridge Canton Mill received authorization to achieve a greater level of HAP
reduction by controlling emissions from the black liquor oxidation (BLOX) system in a new
regenerative thermal oxidizer (RTO) equipped with a wet scrubber for SO2 control. The
modeled SO2 emissions represent the vendor-guaranteed emission rate at the scrubber outlet.
PM and NOx emissions are minimized by proper operating of the RTO and combustion of
natural gas as auxiliary fuel, and no further controls are feasible. The construction of the
RTO/Scrubber has been completed and the equipment they were fully operational prior to the
MACT compliance date of April 17, 2007.
Blue Ridge Paper Products BART determination
19
DAQ has determined that no further analysis of control technologies is required because the unit
is already equipped with the most stringent controls as required by the MACT standards and
permit limits are in place to ensure these controls are operated properly. Therefore, DAQ has
determined that BART for the BLOX is no further controls.
•
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"KULCZYCKI, CRISTINA R
[STL]"
<CRISTINA.R.KULCZYCKI@
MECSGLOBAL.COM>
02/19/2007 02:48 PM
To <Cynthia_Winston@URSCorp.com>
cc
bcc
Subject RE: Quote for Recovery Boiler SO2 Control System
History: This message has been replied to.
Thomas Bell/Austin/URSCorp
07/19/2006 04:16 PM
To Cynthia Winston/Morrisville/URSCorp@URSCorp
cc Trey Pavy/Austin/URSCorp@URSCorp, Blake
Stapper/Austin/URSCorp@URSCorp
bcc
Subject Scrubber support equipment costs
Cyndy,
Attached is a spreadsheet containing rough costs for the equipment about which we spoke over the
phone. These numbers are based on actual purchased equipment and/or budget estimates that were
obtained for similar sized components for some of the AdvaTech projects from first quarter 2006. The
stack price is a lump sum number including construction since that is typically how that item is furnished.
The balance of the numbers are equipment only with no contigency added. I tried to include some
comments in the cells to explain the basis of the numbers in case you needed it.
I hope this helps.
Thanks.
Thomas Bell, P.E.
URS Corporation
512-419-5005 (ph)
512-454-8807 (fax)
This e-mail and any attachments are confidential. If you receive this message in error or are not the intended recipient, you should
not retain, distribute, disclose or use any of this information and you should destroy the e-mail and any attachments or copies.
ncasi NATIONAL COUNCIL FOR AIR AND STREAM IMPROVEMENT, INC.
P.O. Box 13318, Research Triangle Park, NC 27709-3318
Phone (919) 941-6400 Fax (919) 941-6401
Ronald A. Yeske, Ph.D.
President
(919) 941-6404
June 9, 2006
TO: Corporate Correspondents -- CC 06-014
Regional Managers
FROM: Ronald A. Yeske
SUBJECT: Information on Retrofit Control Measures for Kraft Pulp Mill Sources and Boilers
for NOx, SO2 and PM Emissions
The attached document “Retrofit Control Technology Assessment for NOx, SO2 and PM
Emissions from Kraft Pulp and Paper Mill Unit Operations” was prepared to assist NCASI
member company personnel involved in conducting Best Available Retrofit Technology
(BART) site-specific engineering analyses. It deals with the three main pollutants of concern
for BART analyses, namely NOx, SO2 and particulate matter (PM). Potentially available control
technologies for these three pollutants for kraft recovery furnaces, lime kilns and boilers burning
wood, coal, gas, or oil are discussed. Also, control technologies for PM emissions from lime
slakers and smelt dissolving tanks are briefly reviewed.
Sources subject to BART analyses were generally built in the 1962 to 1977 time frame. Thus,
application of any control technologies to these sources will involve retrofits. Even though a
given technology may have been installed on newer more modern units, or may be theoretically
applicable, retrofitting the technology to an older existing unit requires consideration of unit-specific
and location-specific factors. In many situations, these factors would eliminate one or
more control technologies from consideration due to technical infeasibility or excessive costs.
As noted throughout this document, site-specific factors will play a critical role in BART
analyses.
This document does not directly address the cost-effectiveness ($/ton of pollutant removed)
of retrofit control measures. Site-specific information, including capital costs, operating and
maintenance costs, and annual capacity factors, must be considered in assessing the cost-effectiveness
of a given control technology to a particular emission source. Not surprisingly,
the ranges in costs and potential emission reductions are expected to be very large.
For more information on this document, please contact Dr. Arun V. Someshwar, Principal
Research Engineer, at the Southern Regional Center office, phone (352) 331-1745, ext 226;
email asomeshwar@ncasi.org.
Attachment
National Council for Air and Stream Improvement
Retrofit Control Technology Assessment for NOx, SO2 and PM Emissions
From Kraft Pulp and Paper Mill Unit Operations
by Arun V. Someshwar, Ph. D., NCASI
1.0 Introduction
This document summarizes the general applicability of currently available emission control
technologies for NOx, SO2 and particulate matter (PM) to various pulp and paper mill sources.
The three main unit operations in a kraft pulp mill that emit NOx, SO2 and PM are kraft recovery
furnaces, lime kilns and boilers. Boilers can be of the type which burn wood residues alone,
wood in combination with coal, gas or oil, or only fossil fuels. Particulate emissions can also
result from lime slakers and smelt dissolving tanks. Other pulp and paper mill sources for PM are
generally quite insignificant.
The origin and nature of the three pollutants in each relevant pulp mill unit operation is first
discussed. Such discussion should be useful in understanding why some control technologies,
while being suitable candidates for certain unit operations in other industries, may not be suitable
in the pulp and paper industry. It is hoped this document will be useful in the context of a Best
Available Retrofit Technology (BART) site-specific engineering analysis. However, it must be
clearly noted that for any retrofit technology, site-specific considerations for a given emission
source may disqualify a particular control technology from consideration, even though it might
theoretically be feasible or may even have been installed elsewhere on a new, modern unit or a
greenfield operation.
Cost and emission reduction estimates are specifically not covered in this document. However, it
is instructive to consider that a wide range in costs and potential emission reductions are expected
due to the fact that site-specific factors play a critical role in determining how cost-effective
various technologies will be in practice. Many facilities are space-limited, have controls already
in place, or have older combustion equipment that cannot be retrofit to reach required conditions,
making installation of certain technologies problematic or very expensive.
2.0 Kraft Recovery Furnaces
2.1 NOx Control
Compared to coal- or residual oil-fired boilers of similar capacity, NOx emissions from kraft
recovery furnaces are generally quite low, typically in the 60 to 130 ppm range. These low NOx
emissions are due to several factors inherent to kraft recovery furnace operations which include
(a) low nitrogen concentrations in most “as-fired” black liquor solids (generally <0.2% ), (b)
recovery furnace NOx formation resulting predominantly from “fuel NOx” mechanisms
(insufficient temperatures for “thermal NOx” formation), (c) the highly staged combustion design
of recovery furnaces, and (d) the existence of sodium fumes that might participate in “in-furnace”
NOx reduction or removal.
Researchers have concluded that nearly two-thirds to three-fourths of the liquor N is released
during pyrolysis or devolatilization, partly as NH3 and partly as N2, the rest remaining with the
smelt product most likely as a reduced N species. The ammonia released from the black liquor
during pyrolysis partly oxidizes to NO and partly reduces to N2. A review of the theoretical
kinetics governing the reactions between NH3, NO, and O2 suggests that, in the presence of
2 June 4, 2006
National Council for Air and Stream Improvement
excess O2, a decrease in temperature decreases the degree of oxidation of NH3 to NO, thus
implying that fuel NOx generation during black liquor combustion is more temperature-dependent
than previously thought. However, a reduction in furnace temperatures, particularly in the lower
furnace, is generally expected to result in a sharp increase in SO2 emissions from the furnace.
Most of the NO is formed by oxidation of the NH3 volatilized during pyrolysis of the liquor
droplets. Very little NO is formed from the N in the char bed. In certain instances, where the
liquor droplet dries completely before reaching the char bed, additional NO can be formed during
“in-flight” char combustion of the liquor droplet. The use of liquor sprays resulting in larger
droplet sizes avoids the problem of additional NO contribution from char burning.
Some have observed that NOx emissions increased when firing liquors with increasing liquor
solids contents. However, this may have had less to do with thermal NOx or an “in-furnace”
capability of alkali fume to capture NOx as suggested by some, but more to do with a possible
effect on increased conversion of ammonia to NO within the furnace due to an increase in lower
furnace temperatures resulting from firing higher solids liquors.
2.1.1 Low NOx Burners
The use of low-NOx burners (LNB) for black liquor combustion has not been demonstrated.
Unlike fossil fuels, black liquor has a large quantity of water and the drying, pyrolysis, and char
burning of liquor droplets occurs over a long flight trajectory from the liquor guns to the char bed,
thus making unavailable the benefits of staged combustion inherent in LNB designs.
LNBs could however be applied to oil guns or gas burners in recovery furnaces that are used to
supply supplemental heat or for start-up/shut down purposes. However, for most recovery units,
the use of auxiliary fuel is very limited; in such cases the benefit from conversion to LNB would
be marginal.
2.1.2 Staged Combustion
Recent research has concluded that to the extent “staged combustion” is allowed to take place in
the upper furnace during oxidation of the volatilized NH3 to NO, such oxidation can be
minimized. Limited short-term experience after installing “quaternary” air ports in two U.S.
furnaces showed that a 20 to 40% reduction in baseline NOx levels is feasible using such air
staging. However, to make it feasible to install a quaternary air system a recovery furnace
typically needs to be fairly large in size. Thus this option would not be feasible for most BART-eligible
recovery furnaces, since units built in the 1962 t o 1977 time period were considerably
smaller than those installed in subsequent years.
2.1.3 Flue Gas Recirculation (FGR)
Flue gas recirculation (FGR) is also not a viable option for kraft recovery furnaces. In FGR, a
portion of the uncontrolled flue gases is routed back to the combustion zone, primarily with the
intention of reducing thermal NOx. Thermal NOx is, however, not a concern in recovery furnaces,
as discussed earlier. FGR would add additional gas volume in the furnace, increasing velocities
and potentially causing more liquor carryover, which would result in increased fouling of the
recovery furnace tubes.
June 4, 2006 3
National Council for Air and Stream Improvement
2.1.4 Oxygen Trim + Water Injection
Oxygen-trim + water injection, a NOx control technology generally utilized in natural gas-fired
boilers, would not be relevant to kraft recovery furnaces since (1) any injection of water into the
furnace would lead to an unacceptable explosive condition and (2) the oxygen trim technique
would have marginal effect due to the already existing highly staged combustion air configuration
in recovery furnaces.
2.1.5 Selective Non-Catalytic Reduction (SNCR)
At the current time, there is no published information on the extended use of SNCR on an
operating kraft recovery furnace. Short-term tests with the SNCR technology have been reported
in the literature on two furnaces in Japan and one in Sweden. There are a number of critical,
unresolved issues surrounding the use of urea or ammonia injection in a kraft recovery furnace
for NOx control over a long-term basis. A kraft recovery furnace is the most expensive unit
operation in a pulp mill since its primary purpose is to recover chemicals from spent pulping
liquors in a safe and reliable manner. Although steam is generated from liquor combustion,
certain chemical recovery steps have to be accomplished inside the furnace. It is not known
whether the injection of NOx-reducing chemicals into the furnace would have deleterious effects
on the kraft liquor recovery cycle on a long-term basis. Long-term tests would need to be carried
out to address this important issue. In addition, there are several other factors that make the use
of SNCR in a kraft recovery furnace problematic such as (1) the impact of large variations in flue
gas temperatures at the superheater entrance due to fluctuating load and liquor quality, (2) limited
residence times for the NOx-NH3 reactions available in smaller furnaces, (3) impact on fireside
deposit buildup due to reduced chloride purging from long-term NH3/urea use and resulting
impact on tube corrosion and fouling, and (4) potential for significant NH3 slip and plume opacity
problems due to NH4Cl emissions. Unless these concerns are satisfactorily resolved, the use of
SNCR in a kraft recovery furnace should not be considered as a feasible technology.
2.1.6 Selective Catalytic Reduction (SCR)
The use of SCR on a kraft recovery furnace has never been demonstrated, even on a short-term
basis. The impact of high particulate matter concentrations in the economizer region and fine
dust particles on catalyst effectiveness is a major impediment to the application of this technology
ahead of PM control, as is catalyst poisoning by soluble alkali metals in the gas stream. For SCR
installation after an ESP, the gas stream would be too cold for effective reaction with the NOx. A
substantial energy penalty would have to be incurred to reheat the flue gas prior to the SCR
section which would be a major drawback.
2.1.7 Summary
In summary, optimization of the staged combustion principle within large, existing kraft recovery
furnaces to achieve lower NOx emissions might be the only technologically feasible option at the
present time for NOx reduction. However, the effect of such air staging on emissions of other
pollutants, chiefly SO2, CO, and TRS, and other furnace operational characteristics needs to be
examined with longer-term data on U.S. furnaces. Ultimately, the liquor nitrogen content, which
is dependent on the types of wood pulped, is the dominant factor affecting the level of NOx
emissions from black liquor combustion in a recovery furnace. Unfortunately, this factor is
beyond the control of pulp mill operators.
4 June 4, 2006
National Council for Air and Stream Improvement
2.2 SO2 Control
Black liquor contains a significant amount of sulfur, nominally 3 to 5% by weight of the
dissolved solids. While the vast majority of this sulfur leaves the furnace in the smelt product, a
small fraction (generally under 1%) can escape in gaseous or particulate form. Average SO2
concentrations in stack gases can range from nearly 0 to 500 ppm, although most furnaces
currently operate with <100 ppm SO2 in stack emissions. Factors which influence SO2 levels are
liquor sulfidity, liquor solids content, stack oxygen content, furnace load, auxiliary fuel use, and
furnace design. However, none of these factors has exhibited a consistent relationship with SO2
emissions. At the present time, it is generally understood that conditions involving liquor quality
(such as high Btu, high solids liquors) and liquor firing patterns and conditions related to furnace
operations (air distribution, auxiliary fuel, etc.) that lead to maximizing temperatures in the lower
furnace result in minimizing SO2 emissions from kraft recovery furnaces.
There is no experience in the pulp and paper industry with the use of dedicated, add-on flue gas
desulfurization technologies on kraft recovery furnaces. Although there are a few scrubbers on
U.S. kraft recovery furnaces, none of these were installed for SO2 removal. Only one U.S.
recovery furnace does not use an ESP for particulate control; this unit has venturi scrubbers
instead. All of the other scrubbers follow an ESP. Two were installed for heat recovery reasons,
although some SO2 scrubbing may also be occurring especially when caustic is added to the
scrubbing solution. One scrubber following an ESP was installed with the main purpose of
achieving incremental particulate matter removal. Another scrubber following an ESP was
installed on a furnace with a direct contact evaporator to control black liquor droplets being
entrained in the cascade and traveling all the way throughout the ESP and out the stack. Even if
these scrubbers had been installed to reduce SO2 emissions, the removal costs in terms of dollars
per ton of SO2 removed would be large due to high gas flows and site-specific retrofit
considerations. Significant capital would be required for the large gas handling equipment and
additional induced fan capacity needed to overcome the increased pressure drop across the
scrubber.
2.3 Particulate Matter Control
Recovery furnaces are designed and operated in a manner so as to ensure the presence of high
levels of sodium fumes in order to capture the sulfur dioxide produced as a result of oxidation of
reduced sulfur compounds. Consequently, uncontrolled recovery furnace flue gases contain high
levels of particulate matter. The uncontrolled particulate matter load from recovery furnaces is
highly variable and has been reported to range from 100 to 250 lb/ODTP (oven dry ton pulp) for
direct contact evaporator (DCE) furnaces and 200 to 450 lb/ODTP for non-direct contact
evaporator (NDCE) furnaces. The lower particulate loading from DCE furnaces is due to the
capture of some particulate matter in the direct contact evaporator. ESPs built for NDCE
furnaces are designed to compensate for the higher particulate loading.
Particulates generated in the recovery furnace are comprised mainly of sodium sulfate, with lesser
amounts of sodium carbonate and sodium chloride. Similar potassium compounds are also
generated, but in much lower amounts. Trace amounts of other metal compounds, e.g.
magnesium, calcium, and zinc, can be present. A significant portion of the particulate material is
sub-micron in size, which makes removal with additional add-on control devices more difficult.
Increasing liquor firing density (ton/day/ft2) increases recovery furnace particulate loading. Other
factors such as bed and furnace temperature, liquor solids, liquor composition, and air distribution
also affect uncontrolled particulate emissions from recovery furnaces.
June 4, 2006 5
National Council for Air and Stream Improvement
ESPs are the device of choice for controlling PM emissions from kraft recovery furnaces. The
use of larger ESPs is expected to result in better overall PM capture efficiencies. However, this
option is expected to be quite cost ineffective based on the high, site-specific, retrofit costs
incurred. Moreover, with the implementation of MACT II limitations in 2004, most recovery
furnaces are operating at or below NSPS levels (NCASI Corporate Correspondents Memo 01-01).
Any additional benefit would thus be marginal.
3.0 Kraft Lime Kilns
3.1 NOx Control
NOx emissions from lime kilns result mainly from fossil fuel burning (natural gas and fuel oil). A
recent NCASI study involving NOx testing at 15 lime kilns verified that “thermal” NOx was the
sole mechanism operative in gas-fired kilns, while the “fuel” NOx mechanism was mostly
operative in oil-fired kilns. Gas-fired kiln NOx emissions appeared to be strongly dependent on
the dry-end lime temperature. Oxygen availability in the combustion zone was determined to be
the key factor in oil-fired kilns. NOx emissions for gas-fired kilns also exhibited high short-term
variability, unlike for oil-fired kilns. Analysis of long-term daily average data from two lime
kilns showed no difference in NOx emissions between days with and without LVHC NCG
burning. An earlier NCASI study had shown that when stripper off-gases (SOGs) containing
ammonia were burned in lime kilns, a small fraction of the ammonia, up to 23%, converts to NOx.
A BACT analysis conducted for a new lime kiln in 1997 concluded that the use of low NOx
burners in lime kilns was technically infeasible due to complexities resulting in poor efficiency,
increased energy usage, and decreased calcining capacity of the lime kiln. The concept of 'low
NOx burners' is considered a misnomer in the rotary kiln industry. In boiler burners where the
combustion air can be staged, 'low NOx' could be a genuine option. However, in rotary kilns it is
not possible to stage the mixing in the same way. There has to be sufficient primary (burner) air
to provide control in flame shaping although this can be limited to minimize NOx to some extent.
Effectively, the NOx can be reduced to some extent by 'de-tuning' the burner from optimized
combustion. However, the result is an energy penalty by way of a higher heat input per ton
product and higher feed-end temperatures.
Post-combustion flue gas NOx control using SCNR or SCR is not feasible due to the
configuration of the kraft lime kiln. The necessary temperature window of 1500°F to 2000°F for
reagent injection in the SNCR process is unavailable in a kraft lime kiln. The very high PM load
prior to control would make SCR infeasible in advance of the controls and the requisite
temperature window of between 550°F and 750°F for applying SCR after a PM control device is
unavailable for a lime kiln, even for one equipped with an ESP.
Thus, NOx control in newer lime kilns may be achieved mainly by minimizing the hot end
temperatures in gas-fired kilns and by reducing the available oxygen in the combustion zone in
oil-fired kilns, both combustion related modifications. However, these modifications may be
difficult to achieve in certain existing kilns due to their inherent design. For example, in order to
complete the calcining reactions in kilns with short residence times, it is more difficult to control
hot end temperatures in shorter kilns than in longer ones.
6 June 4, 2006
National Council for Air and Stream Improvement
3.2 SO2 Control
Sulfur dioxide is formed in lime kilns when fuel oil or petroleum coke is burned as primary fuel.
SO2 will also be formed if non-condensible gases (NCGs) or stripper off-gases (SOGs) containing
sulfur are burned in the kiln. Lime muds also contain a small amount of sulfur, which when
oxidized, would form SO2. Median sulfur content of concentrated NCGs and SOGs have been
reported as 1.1 and 4.2 lb/ADTP (air dried ton pulp), respectively. Median sulfur contents of 7
lime muds have been reported at 0.2%, which translates to about 1.8 lb S/ADTP. Thus, fossil
fuels such as fuel oil, kraft mill NCG/SOGs, and soluble sulfides in lime mud can contribute a
significant amount of sulfur to the inputs of a lime kiln. Nevertheless, the regenerated quicklime
in the kiln acts as an excellent in-situ scrubbing agent, and venturi scrubbers following the kiln
can further augment this SO2 removal process since the scrubbing solution becomes alkaline from
the captured lime dust. Consequently, even though the potential for SO2 formation in a kiln that
burns sulfur-containing fuels with or without NCGs/SOGs is high, most lime kilns emit very low
levels of SO2 (~50 ppm). Some kilns do, however, occasionally emit higher levels of SO2 (50 to
200 ppm). Not much is known about why this happens.
Emission test data show that SO2 concentrations do not appear to be related to either the fuel type
(oil, gas) or the presence or absence of concentrated NCG or SOG burning in the kiln. A
preliminary sulfur input-output balance carried out on 25 kilns with wet scrubbers and 7 kilns
with electrostatic precipitators (ESPs), with sulfur inputs from fuel oil, NCGs and SOGs, or just
lime mud, showed over 95% of the SO2 generated from the oil, NCG/SOGs, or lime mud was
captured within the kiln. For kilns with wet scrubbers (majority) that have high SO2 emissions,
alkali addition to the scrubbing fluid could further reduce the SO2 emissions.
3.3 Particulate Matter Control
While passing through the kiln, the combustion gases pick up a good deal of particulate matter
both from lime mud dust formation and from alkali vaporization. This PM must be removed
before the gases exit to the atmosphere. Mechanical devices such as dust chambers or cyclones
are generally used to remove larger particles, which are mainly calcium-containing. A wet
scrubber or electrostatic precipitator follows for removal of smaller particulates, which are mainly
sodium sulfate and sodium carbonate and have aerodynamic diameters less than 10 μm.
Kraft lime kiln PM emissions are typically controlled by venturi-type wet scrubbers. Scrubbers
with increasingly better PM removal efficiencies, such as the Ducon Dynamic Wet Scrubber,
have been installed up until the late 1980s. However, most of the PM control installations on
lime kilns since about 1990 have been ESPs. Replacing a wet scrubber with an ESP will most
likely reduce PM emissions, but may increase emissions of SO2. The wet scrubber acts as an
additional alkaline SO2 scrubber since it captures alkaline PM leaving the kiln. Just as for
recovery furnaces, with the implementation of MACT II limitations in 2004, most lime kilns are
operating at or below NSPS levels. Any additional benefit would thus be marginal.
4.0 Boilers
The majority of pulp and paper industry boilers are combination boilers, in that they are designed to
burn more than one fuel. Thus, it should be noted that while a particular technology may be beneficial
for a particular pollutant, the same technology may not address the control of another pollutant. For
example, a wood-fired boiler with a wet scrubber for PM control may obtain better PM control with
an ESP. However, if the boiler also fires some sulfur-containing fuel (as is often the case), the
SO2 removal capability of the wet scrubber will be sacrificed by the installation of an ESP.
June 4, 2006 7
National Council for Air and Stream Improvement
4.1 Natural Gas-Fired Boilers
Gas-fired boilers are usually not equipped with particulate collectors. SO2 emissions depend on
the sulfur content of the gas, which is typically negligible. NOx emissions are dependent on the
combustion temperature and the rate of cooling of the combustion products. There are several
combustion modification techniques available to reduce the amount of NOx formed in natural
gas-fired boilers and turbines. The two most prevalent ones are flue gas recirculation (FGR) and
low-NOx burners. FGR reduces formation of thermal NOx by reducing peak temperatures and
limiting availability of oxygen. Low-NOx burners reduce formation of thermal NOx by delayed
combustion (staging) resulting in a cooler flame. In conjunction with FGR, the burners can
achieve NOx emission reductions of 60 to 90%. Other techniques include staged combustion and
gas reburning. In general, these techniques have been incorporated in newer boilers and thus
their NOx emissions are lower than those of older units.
There are also add-on control technologies that can reduce NOx emissions from gas-fired boilers
such as selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR).
However, since most of the pulp and paper industry gas-fired boilers are of the package boiler
type, cost considerations typically make the use of such technologies cost ineffective. Further,
both the SNCR and SCR technologies have not been proven to apply to industrial boilers with
frequent swing loads.
4.2 Fuel Oil-Fired Boilers
For fuel oil-fired boilers, criteria pollutants can be controlled by fuel substitution/alteration,
combustion modification and post-combustion control. Fuel substitution reduces SO2 and NOx
and involves burning an oil with lower S or N content, respectively. Particulate emissions are
lower when burning lower sulfur content oils, especially distillate oil.
4.2.1 NOx Control
For boilers burning residual oil, fuel NOx is the dominant mechanism for NOx formation and thus
the most common combustion modification technique is to suppress combustion air levels below
the theoretical amount required for complete combustion. There are several combustion
modification techniques available to reduce the amount of NOx formed in fuel oil-fired boilers,
including low excess air, burners out of service, biased-burner firing, flue gas recirculation,
overfire air, and low-NOx burners. NOx reductions that could range between 5 and 60% from
uncontrolled systems may be expected from using these techniques.
Post-combustion controls include SNCR and SCR. NOx reductions from 25 to 0% and from 75 to
85% may be expected from use of SNCR and SCR systems on oil-fired boilers, respectively.
However, just as for gas-fired boilers, most of the pulp and paper industry oil-fired boilers are of
the package boiler type, and cost considerations typically make the use of such technologies cost
ineffective. Furthermore, both the SNCR and SCR technologies have not been proven to apply to
industrial boilers with frequent swing loads.
4.2.2 SO2 Control
SO2 emissions are controlled by a number of commercialized post-combustion flue gas
desulfurization (FGD) processes which use an alkaline reagent to absorb SO2 in the flue gas and
produce a sodium or calcium sulfate compound. The FGD technologies may be wet, semi-dry or
dry depending on the state of the reagent as it leaves the absorber vessel.
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4.2.3 Particulate Matter Control
Due to the extremely low level of PM emissions, most residual oil-fired boilers do not have
particulate matter controls. A few boilers are, however, equipped with mechanical collectors or
ESPs.
4.3 Coal-Fired Boilers
4.3.1 NOx Control
NOx emissions from coal-fired boilers can be controlled by a) combustion controls and b) post-combustion
controls. Combustion controls involve a) reducing peak temperatures in the
combustion zone, b) reducing gas residence time in the high-temperature zone, and c) air or fuel
staging by operating at an off-stoichiometric ratio by using a rich fuel-air ratio in the primary
flame zone and lower overall excess air conditions. The use of combustion controls depends on
the type of boiler and the method of coal firing. Low-NOx burners and overfire air (OFA) have
been successfully applied to tangential- and wall-fired units, whereas reburning is the only current
option for cyclone boilers. For large base-loaded coal-fired boilers, the most developed and
widely applied post-combustion NOx control technology is SCR. Catalyst deactivation and
residual NH3 slip are the two key operating considerations in an SCR system. There is only
limited experience with the use of SNCR systems on industrial coal-fired boilers. NOx reductions
from 30-70% and from 60-90% may be expected from use of SNCR and SCR systems on base-loaded
coal-fired boilers, respectively. SNCR has a narrow temperature window in which it is
effective, in the 1500 to 1900°F range, and SCR has a similar, but lower temperature window of
550 to 750°F. When applied to industrial boilers, neither the SNCR nor the SCR technologies
have been proven to yield the same high NOx removal efficiencies expected when the boilers
operate at base loads as when they operate with frequent swing loads. The inability to maintain
good control within the required temperature window during swing loads is most likely
responsible for this reduction. Most coal-fired boilers in the pulp and paper industry operate in
the swing load mode, a function of supplying steam as required to the various components of the
process.
4.3.2 SO2 Control
Just as in fuel oil combustion, criteria pollutants can be controlled by fuel substitution/alteration,
combustion modification and post-combustion control. SO2 reductions can be achieved by
burning a coal with lower S content. SO2 emissions can be controlled by a number of
commercialized post-combustion flue gas desulfurization (FGD) processes which use an alkaline
reagent to absorb SO2 in the flue gas and produce a sodium or calcium sulfate compound. The
FGD technologies may be wet, semi-dry or dry depending on the state of the reagent as it leaves
the absorber vessel. The pulp and paper industry has limited experience with operating FGD
systems on coal- or oil-fired boilers. Retrofit considerations include space restraints in many
facilities.
4.3.3 Particulate Matter Control
Particulate emissions from coal-fired boilers are controlled by using a) ESPs, b) fabric filters (FF)
or c) venturi scrubbers. Multi-cyclones are generally used as precleaners upstream of more
efficient ESPs or FFs. The key operating parameters that influence ESP performance include fly
ash mass loading, particle size distribution, fly ash resistivity (which is related to coal sulfur
content), and precipitator voltage and current. Data for ESPs applied to coal-fired boilers show
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fractional collection efficiencies greater than 99% for fine (<0.1μm) and coarse particles (>10
μm) and a reduction in collection efficiency for particles between 0.1 and 10 μm. Operational
parameters that affect fabric filter collection efficiency include air-to-cloth ratio, operating
pressure loss, cleaning sequence, interval between cleanings, cleaning method, and cleaning
intensity. Collection efficiencies of fabric filters can be as high as 99.9%. Scrubber collection
efficiency depends on particle size distribution, gas side pressure drop through the scrubber, and
water (or scrubbing liquor) pressure, and can range from 90 to 95% for a 2 μm particle.
4.4 Wood-Fired Boiler Emissions
4.4.1 NOx Control
Most large wood-fired boilers used in the pulp and paper industry are of the spreader stoker
design. NOx control technologies effective for use on gas and oil burners are not applicable to
spreader-stoker design boilers. Furthermore, these boilers are often operated handling swing
loads, which makes add-on NOx controls difficult to implement. Spreader stoker boilers
inherently practice staged combustion, which lowers NOx emissions, but within limits.
Fuel NOx is the dominant NOx formation mechanism operative during wood combustion. Fuel
NOx is most efficiently controlled by staged combustion. Overfire air ports inherent to most
spreader-stoker boilers provide for staged combustion. The underfire and overfire air are
balanced in most wood-fired spreader stokers to control NOx.
As with other fuels, potential post-combustion controls include SNCR and SCR. SNCR has been
applied to a few base-loaded wood-fired boilers, mainly in the electric generating industry.
However, its long-term efficacy on wood-fired boilers with changing loads has not been
demonstrated. Experience in the pulp and paper industry to date has shown it has been used on
occasions for polishing, to get perhaps 10-20% NOx reduction during periods of air quality
problems. The problem with control of the required temperature window is an inherent difficulty
with use of SNCR for load-following boilers, whether wood or fossil fuel. Inadequate reagent
dispersion in the region of reagent injection in wood-fired boilers is also a factor mitigating
against the use of SNCR technology. At least one pulp mill wood-fired boiler met with
significant problems and had to abandon their SNCR system. Significant ammonia slip, caused
by inefficient dispersion of the reagent within the boiler, was to blame.
The use of SCR on wood-fired boilers operating in the forest products industry has also never
been successfully demonstrated for spreader stoker boilers, and would face the same inherent
problem of requiring it to be post PM-control to protect the catalyst, and achieving and
maintaining the required temperature window for effective NOx control.
4.4.2 Particulate Matter Control
Particulate matter is the air pollutant of primary concern in wood-fired boilers. As for coal-fired
boilers, the most common devices used to control particulate emissions from wood-fired boilers
are wet scrubbers and electrostatic precipitators (ESPs). Fabric filters (FF) and the electrified
gravel bed filter (EGF) have been used on a few units. Wet scrubbers are widely used, operating
at gas pressure drops ranging from 6 to 25” H2O. Liquid to gas ratios in the venturi system
typically range from 8 to 10 gal H2O/1000 acfm saturated. Solids buildup in the recirculation
loop rarely is allowed to exceed 5% by weight. High carbon ash resulting from wood combustion
is more difficult to remove with an ESP due to its high conductivity/low resistivity. Thus,
specific collection areas (ratio of ESP plate area to gas flow volume through the ESP) for ESPs
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National Council for Air and Stream Improvement
on wood-fired boilers are greater than for those for coal-fired boilers, ranging from about 300 to
500 ft2/1000 acfm. Power requirements range from 150 to about 400 watts per acfm. To address
fire concerns, ESPs on wood-fired boilers are sometimes operated in the wet mode, where the
collection plates and internal parts are wetted continuously with water. A pre-quench is generally
used to saturate the gas stream. Fabric filters are rarely used on wood-fired boilers due to
concerns about bag flammability. Fabric filters have been successfully used where bark from
logs stored in salt water is burned and the salt reduces the fire hazard. In this situation, the fabric
filter is effective in removing the very small salt particulates exiting the boiler. Gravel-bed filters
have a slowly moving bed of granular “rock” as the filtration medium through which the flue gas
must travel. These systems are electrostatically augmented (10 to 20 watts/1000 acfm). A high
voltage (about 50 kV) is applied to an electrical conductor positioned within the bed and this
creates an electrical field between the conductor and the inlet and outlet louvers. Particulate
collection efficiencies for wood-fired boilers range from 65 to 95% for two multiclones in series,
over 90% for wet scrubbers, from 93 to 99.8% for ESPs and FFs and about 95% for EGFs. Once
again, it should be noted that most wood-fired boilers are combination boilers that may burn other
sulfur-containing fuels. Thus, a change in the control device might affect the ability to control
other pollutants. For example, replacing a wet scrubber with an ESP for better PM control would
result in higher SO2 emissions from a boiler burning wood in combination with oil or coal.
5.0 Other Source Emissions
5.1 Slakers - PM emissions
Slakers are generally vented through a stack to discharge the large amounts of steam generated.
The steam may contain particulate matter, which is largely calcium and sodium carbonates and
sulfates. Scrubbers are generally employed to capture this particulate matter. Other PM control
devices such as ESPs and fabric filters are both technologically infeasible (very high moisture
source) and not cost effective.
5.2 Smelt Dissolving Tanks - PM Emissions
As with the recovery furnace, particulate emissions from smelt tanks are comprised of mainly
sodium compounds with much lesser amounts of potassium compounds and some other trace
metal compounds. The dominant compound is sodium carbonate, followed by sodium sulfate.
Roughly 90% (by weight) of the particles have equivalent aerodynamic diameters under 10 μm,
and 50% have diameters under 1 μm. Most smelt tank PM emissions are controlled by wet
scrubbers, many of which are wetted fan scrubbers that are very effective in removing fine
particulate. A dry ESP is once again infeasible as an option due to the high moisture content of
the gases. The wet scrubber also serves to control total reduced sulfur compound emissions
through pH control, thus replacing it with a wet ESP is not an option. As noted for other kraft
mill sources, MACT II Implementation in 2004 has also resulted in significantly reduced
allowable PM emissions from smelt dissolving tanks.
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